BEFLBXEfi l\ Till SPINAL WI.MAI. WD BPLNAL SHOCK 



That the nociceptive reflexes should be among the firsl to return after 

 spinal transection is of considerable interesl as indicating their im- 

 portance in the protection of the animal from injury. They are the 

 essentia] reflexes of defense, and it is considerably later in the recov 

 of the animal before reflexes dependent upon stimulation of other tac- 

 tile receptors begin to show themselves. The most importanl of this 

 latter group of more special reflex movements include the so-called 

 scratch reflex and the extensor thrust. The scratch - its name 



implies, is the scratching movemenl of flexion and extension of the hind 

 limb at a rate of about four contractions per Becond that occurs when 

 a mechanical stimulus is applied to the flank and shoulder area of the 

 animal. For example, if we gently draw a pencil or the fingers back- 

 ward and forward among the hairs on this region of the spinal animal. 

 the corresponding hind limb will be broughl up so thai the claws are 

 approximately at the place stimulated, and the limb thus directed will 

 undergo a series of flexions and extensions, designed evidently for the 

 purpose of scratching the area of skin that has been stimulated, [f the 

 stimulus is a weak one, only the initial stages of the movement may 

 occur, such as the preliminary flexion of the leg. As we. have already 

 stated, the receptive stimulus calling forth this reflex is very specific 

 in nature. A pinprick or rough friction of the reflex area will not produce 

 it, nor will the application of heat or of a single electric shock. The 

 most adequate stimulus is one simulating as nearly as possible the con- 

 dition which would he produced by the movement on the Hank of the 

 animal of some insect. This more or less complicated scratch reflex can 

 of course also he elicited in animals whose spinal cord has not been cut, 

 but we can U01 predict in such cases whether the reflex will occur. Tin* 

 brain may inhibit the reflex arc and prevent the movement. In a spinal 

 animal, however, the reflex always occurs provided an adequate stimulus 

 is applied. The greal importance of the scratch reflex in the study 

 the physiology of the spinal cord tests in the Pad thai a large stretch 

 of cord is involved in the reflex path. The afferenl impulses must enter 

 at a much higher level than the efferent impulses leave, and b< ' 

 these two points there must exisl a long intraspinal neuron ' sec p 

 813). This permits us in study many conditions influencing reflex action 

 which otherwise in a reflex located in one segment only it would he im- 

 possible to invest igate ' 



The extensor thrust is elicited by applying pressure to the pad of the 



paw or the soh' of the foot. Tl consists of a quick extension movement 



of the corresponding limb usually with a flexion of tin' opposite limb. 



After complete recover*) iY"m shock, the paralyzed parts of the bod 

 are capable of performing even more complex movements than those al- 



